Shamrock,
If you are just thinking about converting a PPL (as you seem to be) then conversion to a JAR PPL here in the UK is quite straightforward. See the thread
here and follow its links to the excellent Irv Lee's site.
In a nutshell, you'll have to do some or all of the UK PPL exams (depending on whether you have 100 hours or not), do the skills test and have a medical.
Groundhog's alarming figures are true for commercial and IR conversions, but you don't seem to be asking about that.
You imply that you already have some flight training. I'd check whether any of those hours will count towards a NZ licence - they may not. New Zealand PPLs require a minimum of 50 hours.
As far as schools and clubs in NZ go, I've only flown with one - Kapiti Aero Club at Paraparaumu, just north of Wellington. I thoroughly enjoyed that - an excellent bunch of people, great scenery nearby and enough varied terrain to start on things like mountain flying as well as the basics. A UK-based friend who did her PPL(H) there last year also had a great time with them.